The first American ambassador to Syria since 2005 arrived in Damascus today at a time of regional turmoil and with Syrian-US relations still mired in mutual distrust.Few expect immediate changes, but having career diplomat Robert Ford in Damascus offers Washington a better glimpse into Syria at a time of rising tensions – particularly in neighbouring Lebanon, where the western-backed government collapsed last week.

"Intelligence sharing is the most promising overlap in US-Syrian relations," said Joshua Landis, an American professor and Syria expert. He noted that like Washington, Syria's secular regime is against al-Qaida and "takfiri" Islamists, referring to an ideology that urges Sunni Muslims to kill anyone they consider an infidel.

President Barack Obama's administration has argued that returning an ambassador to Damascus would help persuade Syria to change its policies regarding Lebanon, Israel and Iraq, and end its support for extremist groups.

Syria is designated a "state sponsor of terrorism" by the state department.

Ford takes up his post just days after the government in Lebanon collapsed when Hezbollah, which gets key support from Syria and Iran, walked out of the cabinet on Wednesday.

The government collapsed after months of tensions stemming from a UN-backed investigation into the assassination of former Lebanese prime minister Rafik Hariri. Many have blamed the killing on Syria and Hezbollah. President George W. Bush's administration withdrew a full-time ambassador from Syria in 2005 in part to protest Hariri's assassination.

Both Syria and Hezbollah deny any links to the assassination, which galvanised opposition to Damascus in 2005 and prompted huge street demonstrations that helped end Syria's 29-year military presence in Lebanon and paved the way for pro-western parties – led by Saad Hariri, the murdered man's son – to head the government in subsequent elections.

The tribunal is expected to issue indictments soon.

With Syria's backing, Hezbollah has demanded that Saad Hariri break off Lebanon's ties with the tribunal, but he has refused. The collapse of his government on Wednesday was a clear sign of the strength of Hezbollah – along with its Syrian and Iranian patrons – and a setback for US policy in the region.

Obama nominated Ford, a former ambassador to Algeria, to the post in February.

The nomination stalled after Ford's confirmation hearings, but Obama bypassed the Senate in December and directly appointed Ford and three other new US ambassadors whose nominations had been stalled or blocked by lawmakers for months.

A number of senators objected because they believed sending an ambassador to Syria would reward it for bad behaviour.

Syria has bounced back from years of international isolation and is wielding its influence in crises around the Middle East, shrugging off US attempts to pull it away from its alliances with Iran, Hamas and Hezbollah.

Washington has increasingly expressed its frustration with Syria, which it says is stirring up tension through its support of Hezbollah. In October, HillaryClinton, the secretary of state, said Syria's behaviour "has not met our hopes and expectations".

Syria could benefit from improved ties with Washington, which would boost its economy and end sanctions first imposed by Bush.

Bilal al-Ghazzawi, a 23-year-old working at an electronics shop, said he was doubtful relations between the two countries would change."Americans cannot be trusted," he said. "Today they send an ambassador, tomorrow they might pull him out again."AP Beirut